Jorhat, July 19: A rumble was all they heard before the ground beneath their feet gave way, sending 15 students of a girls’ college in this Upper Assam town hurtling down an almost 10-feet crater that inexplicably appeared where the concrete floor of their classroom had been seconds earlier.

Philosophy teacher Jyoti Devi was about to begin her lecture in classroom number 15 of Devicharan Baruah Girls’ College when she and the 26 students in front of her felt a tremor resembling an earthquake, not uncommon in these parts.

Before she or any of the girls could react, a large portion of the floor opened up. “I found myself staring helplessly as the gaping hole just swallowed 15 of my students along with the desks and benches,” Jyoti Devi told The Telegraph.

Of the dozen girls who were injured, two were in a serious condition until late tonight.

Silpi Phukon, one of the victims, said she felt the floor rattle before the crevice took her and the other girls in. “It will haunt me for a long time.”

Mitali Barua appeared shell-shocked, too. “It happened so suddenly... my only thought then was to come out of that dark hole,” she said.

Mitali looked up and saw her classmates gather around the rim of the crater, stretching their hands to help those who were down below. “I climbed onto the benches and the desks and chunks of concrete before they pulled me out. I was the first to come out.”

It transpired that the cave-in was triggered by the Tarajan Noi, a rivulet that has changed course over the years and now flows barely two metres from the old college building in which the incident occurred. “The rivulet may have loosened the soil, leading to the cave-in,” a resident of the area said.

Constructed about three decades ago, the old building houses three classrooms, a canteen and the girls’ common room. The building was about 15 metres from the rivulet when it was built, but encroachment on the other side led to a change in course.

Hours after the near-catastrophe, the college management admitted to being aware that the entire building might cave in like the floor of one classroom did today. “I have asked for the old building to be vacated immediately,” principal Hem Chandra Hazarika said.

The principal claimed that the district administration and the Jorhat Development Authority had been informed of the danger to the building from the Tarajan Noi. “We knew the rivulet could cause damage because of a change in course, but we never thought the impact would be so sudden and so scary.”

Director of higher education A.K. Sahoo asked the inspector of schools to compile a report on the incident, while deputy commissioner (in-charge) D.K. Nath described the incident as an “unfortunate” one. “But this has given us the opportunity to clear encroachment near all the rivulets flowing through Jorhat town,” he said.

Chief minister Tarun Gogoi, who visited Jorhat earlier this week, was apparently shocked to find knee-deep water in parts of the town and instructed the public works department to draw up a plan to solve the problem.

Gogoi was told that the growth of slums along the rivulets, which are the drainage arteries of the town, was a reason for floods.